1. Field of the Invention
The present invention relates to a vehicle travel path indicating apparatus, and more particularly to a path data storage system serving as a fixed range indicating system for use in a vehicle travel path indicating apparatus.
2. Description of the Prior Art
There have been known and used many different locational data sources for providing two-dimensional coordinates which represent the position of a moving vehicle and are continuously updated. One of the known locational data sources is composed of a range or distance sensor for generating a signal dependent on the distance that the vehicle has traveled, an azimuth sensor for generating a signal dependent on the heading of the vehicle, and a computer or an electric circuit for processing the signals from these sensors to issue vehicle locational data. Since such a locational data source is relatively small in size, less costly to construct, and requires no external equipment such for example as a reference-point wave transmitting station, it is suitable especially for use in a navigation system for small-size vehicles such as automobiles. The locational data source of this type is employed in a navigation system disclosed in U.S. Pat. Nos. 4,139,889 and 3,789,198.
The navigation system revealed in U.S. Pat. No. 4,139,889 comprises a locational data source and a display such as a CRT. In the disclosed navigation system, a point indicating the position of the vehicle is plotted on the display in accordance with locational data issued from the locational data source.
There are also known improved navigation systems which display the path that the vehicle has traveled as well as the current vehicle position. These improved navigation systems are advantageous in that the travel path can be recognized, and also in that even when vehicle locational data are incorrect due to an error caused by the locational data source, a relatively correct vehicle location can be deduced by comparing the features of a travel path pattern indicated on the display with those of a road pattern on a map (which may be superimposed on the display screen. The improved navigation systems comprise a locational data source for issuing vehicle locational data which are continuously updated, a memory for sequentially storing the vehicle locational data as travel path data, and a display unit for plotting a series of dots indicative of the travel path of the vehicle on a display such as a CRT. Such navigation systems are shown in U.S. Pat. Nos. 4,071,895, 4,400,780, and 4,402,050.
The prior navigation systems however have had the following problem, i.e., although the actual location of the vehicle can be deduced more correctly if the storage intervals of locational data are rendered so short that the path is indicated with a continuous smooth curve, such shortening of the storage interval requirs a larger-capacity memory, a larger-size system, and a higher cost of manufacture.